Adult onset asthma

Celiac can be caused my an infection, IIRC. However, the effects should be localized. There also exists plain old wheat allergy, which will not destroy your intestines like celiac, but still cause discomfort. From what I hear, food allergies can manifest anywhere, so maybe this is your issue.

I guess it may be time to go ahead and take an allergens test for certainty. Even though they aren't 100%, I feel a skin prick test wouldn't be the same as if they had a more invasive method of detecting conflicts such as that.